The present invention relates to an apparatus for executing high-efficiency load tests on a multiplicity of electronic components over many hours in a high temperature environment while realizing a reduction in the space required for installation of testing equipment.
With the recent amazing diffusion of microcomputers in a variety of fields covering from factories to homes, there has arisen a severe requirement for high reliability of electronic components incorporated in such microcomputers. It is therefore essential to conduct strict inspection and load testing of the electronic components prior to incorporation thereof in the microcomputers. Considering an infinite variety of circumstances under which the computers are used, the load test needs to be executed for several or more hours continuously in a high temperature environment.
However, in the conventional load testing apparatus known heretofore, there are existent the following disadvantages:
(1) Batch type load testing apparatus
A load test for electronic components such as printed circuit boards is carried out by first inserting them in magazine racks, then carrying the racks into a load testing thermostatic room at 40.degree. C. or so by an operator either manually or with the aid of an auxiliary device, and subsequently energizing the components for a predetermined period of time.
In such a testing apparatus, raising the room temperature further than 40.degree. C. or so is not permitted so as to avoid deterioration of the working environment for the operator. The load test extending over many hours causes harmful influence to the operator's health. Furthermore, it is impossible to achieve fast progress in handling a large amount of electronic components using such an apparatus.
(2) Conveyor type load testing apparatus
This type executes a load test by inserting electronic components in magazine racks and, with storage transport thereof into a thermostatic room, energizing the components from a current collector located below the magazine racks. In such arrangement where a conveyor driving mechanism, a storage transport mechanism and so forth are subjected to the high temperature in the load testing thermostatic room, it is unavoidable that the reliability of the apparatus function is reduced with deterioration of the maintainability. Consequently, this type of apparatus is considered to be unsuitable for use under high-temperature testing condition. Furthermore, there occurs sparking due to momentary current interruption between the current collector and the joint of pallets having the magazine racks mounted thereon, hence inducing failure in attaining stable current conduction. In addition, since the flowing state of air enveloping the electronic components in the magazine rack at a standstill is different from that enveloping the components in any other magazine rack in motion, a difference is caused between the surface temperature distributions due to the heat generated from the electronic components. Consequently, it is impossible to retain a uniform surface temperature distribution of all of the components under control.
(3) Stationary shelf type load testing apparatus
In this apparatus, stationary shelves are installed in a high temperature room, and magazine racks with electronic components inserted therein are carried into and out of such room by means of a stacker crane. However, in the stage of transferring the magazine racks onto the shelves, it is necessary to perform an operation of switching on and off the power supply between the magazine racks and the shelves. Moreover, driving the stacker crane in a high temperature room brings about reduction in the reliability of the apparatus with deterioration of the maintainability due to the harmful effect that results from such high temperature. Furthermore, when an unbalanced state is induced with respect to the distribution of the magazine-mounted components above shelves and the non-mounted ones, there occurs a difference in the states of circulation of high temperature air, hence causing difficulties in making the temperature uniform throughout the thermostatic room. As a result, a satisfactory load test is not achievable for all of the electronic components under uniform temperature conditions.
In view of such circumstances, the present invention has been accomplished with elimination of the above-mentioned disadvantages observed in the conventional load testing apparatus. Hereinafter the invention will be described in detail with reference to the accompanying drawings.